A possible case of sporadic aurora observed at Rio de Janeiro

TL;DR

This paper reports a historical observation of a potential sporadic aurora in Rio de Janeiro in 1875, analyzing spectroscopic and visual data to classify it as a rare low-latitude aurora event during low magnetic activity.

Contribution

It presents a detailed analysis of a historical low-latitude aurora, expanding knowledge of sporadic aurora occurrences in South America during quiet magnetic conditions.

Findings

Event likely a sporadic aurora based on spectroscopic and visual analysis.

No worldwide aurora reports on that day, indicating low magnetic activity.

Adds a new case of sporadic aurora in the South American sector.

Abstract

Being footprints of major magnetic storms and hence major solar eruptions, mid- to low-latitude aurorae have been one of the pathways to understand solar-terrestrial environments. However, it has been reported that aurorae are also occasionally observed at low latitudes under low or even quiet magnetic conditions. Such phenomena are known as "sporadic aurorae". We report on a historical event observed by a scientist of the Brazilian Empire in Rio de Janeiro on 15 February 1875. We analyze this event on the basis of its spectroscopic observations, along with its visual structure and coloration, to suggest this event was a possible case of sporadic aurorae. Given the absence of worldwide aurora observations on that day as a consequence of low magnetic activity recorded on the days preceding the observation, in addition to a detailed description, the event observed can most likely be classified as a sporadic aurora. We discuss the geographic and magnetic conditions of that event. Thus, we add a possible case of sporadic aurora in the South American sector.